A terahertz imager is an image sensor adapted to capture an image of a scene based on waves in the terahertz frequency range. In general, terahertz waves are considered to comprise waves having a frequency of between 300 GHz and 3 THz. These frequencies for example correspond to wavelengths of one millimeter or less. For example, a 1 THz wave has a wavelength of approximately 300 μm.
Terahertz imagers are used widely for applications in which it is desirable to “see through” certain materials. In particular, terahertz waves have good penetrability in many dielectric materials and non-polar liquids. They are however almost entirely reflected by metals and absorbed by water molecules. This makes terahertz imagers particularly suited for applications such as in the security scanners used at airports and in devices used to analyze works of art. The wavelength is in general short enough to achieve good spectral resolution for imaging, but long enough such that the waves are scattered relatively little by air particles such as dust or smoke.
In general, terahertz imagers use a terahertz source to illuminate the scene to be captured. This is because the presence of natural terahertz radiation is generally relatively low.
It has been proposed to provide a fully integrated terahertz camera based on silicon technology. However, there are technical difficulties in implementing such a camera, due at least in part to the relatively high frequency of the terahertz signal range, and the relatively low energy of the signal to be captured. Furthermore, it would be desirable to adapt terahertz imagers to permit them to additionally capture image depth and/or to improve the image quality.